Separation of chloropentafluoroethane from pentafluoroethane

ABSTRACT

Separation of CClF 2  CF 3  from CHF 2  CF 3  is effectively achieved using either acidic inorganic molecular sieves, non-acidic silicate molecular sieves, or activated carbon.

FIELD OF THE INVENTION

This application is a 371 of PCT10543/03203 filed Apr. 6, 1993.

This invention relates to the separation of mixtures of halogenatedhydrocarbons containing fluorine, and more particularly to theseparation of chloropentafluoroethane (i.e., CClF₂ CF₃ or CFC-115) andpentafluoroethane (i.e., CHF₂ CF₃ or HFC-125).

BACKGROUND

Products containing pentafluoroethane (i.e., pentafluoroethane products)are produced in various degrees of purity. HFC-125 is usually preparedby chlorofluorinating perchloroethylene to produce a mixture including1,1,2-trichlorotrifluoroethane (CFC-113), 1,2-dichlorotetrafluoroethane(CFC-114) and 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123); removing1,1,2-trichlorotrifluoroethane; and fluorinating the remaining mixtureby various processes to produce a product containing pentafluoroethane(HFC-125) and chloropentafluoroethane (CFC-115) as well as smalleramounts of other fluorinated compounds (e.g., hexafluoroethane, FC-116).Various other methods for making pentafluoroethane also result inmixtures with significant amounts of chloropentafluoroethane. Forexample, HFC-125 can be produced by the hydrogenolysis of CFC-115 (see,e.g., Japanese Kokai No. 03/099026).

HFC-125 is a valuable non-chlorine containing fluorocarbon that isespecially useful as a refrigerant, blowing agent, propellant, fireextinguishing agent or sterilant carrier gas. It has been found that formany of these applications, the presence of CFC-115 can significantlyalter the physical properties of HFC-125. Furthermore, CFC-115 as achlorine-containing halocarbon can reportedly have a deleterious effecton the stratospheric ozone layer. As a result, there have beencontinually increasing market and process demands for high purity CHF₂CF₃. Consequently, identification of methods of separation represents asignificant aspect of preparing HFC-125 for specific applications.

Purification of halogenated hydrocarbon products has been the subject ofconsiderable research. Of particular interest are the challengespresented in separating a halogenated hydrocarbon from materials such asimpurities in the starting materials used to produce the halogenatedhydrocarbon, excess reactants, and reaction co-products and by-productswhich are difficult to remove by standard separation methods such asdistillation. Mixtures of pentafluoroethane and chloropentafluoroethanecan be nearly azeotropic. The boiling points of the halogenatedhydrocarbons are very close (-48.5° C. for pentafluoroethane and -38.7°C. for chloropentafluoroethane). Furthermore, their relative volatilityis below 1.1 at concentrations of pentafluoroethane greater than 87.5mole percent and below 1.01 at concentrations of pentafluoroethanegreater than 95 mole percent. The boiling points and relativevolatilities indicate that it is extremely impractical to recoversubstantially pure pentafluoroethane from such mixtures by simpledistillation.

Both carbon based and zeolite based sorbents have been proposed forvarious separations. The effectiveness of separation with either sorbentvaries with the chemical components and the sorbents involved. Thesuccessful design of sorbent based systems is considered highlydependent upon experimental determination of whether the relativesorbencies of the particular compounds are suitable for such systems.

SUMMARY OF THE INVENTION

We have found that mixtures of CClF₂ CF₃ (CFC-115) and CHF₂ CF₃(HFC-125) can be substantially separated by using a sorbent for CClF₂CF₃ selected from the group consisting of (i) acidic inorganic molecularsieves (e.g., zeolite Y having an intermediate electronegativity greaterthan 2.8), (ii) non-acidic silicate molecular sieves (e.g., silicalite),and (iii) activated carbons. The present invention provides a processfor separating a mixture of CHF₂ CF₃ and CClF₂ CF₃ to provide a productwherein the mole ratio of CHF₂ CF₃ relative to CClF₂ CF₃ is increasedwhich comprises contacting said mixture with said sorbent at atemperature within the range of -20° C. to 300° C. and a pressure withinthe range of 10 kPa to 3000 kPa and for a period of time sufficient toremove a substantial amount of the CClF₂ CF₃. As a result, the moleratio of CHF₂ CF₃ to CClF₂ CF₃ increases (preferably such that therelative amount of CFC-115 in the product is no more than 50% of therelative amount of CFC-115 in the initial mixture); and a productwherein the mole ratio of CHF₂ CF₃ relative to CClF₂ CF₃ is increased,may thus be recovered. The present invention provides a process forproviding a high purity HFC-125.

This invention also provides a process for separating a mixture of CClF₂CF₃ and CHF₂ CF₃ to provide a product wherein the mole ratio of CClF₂CF₃ relative to CHF₂ CF₃ is increased which comprises contacting saidmixture with said sorbent as described above to remove a substantialamount of the CClF₂ CF₃, and desorbing sorbed CClF₂ CF₃ to provide aproduct which is enriched therewith. Said process for producing a CHF₂CF₃ enriched product and said process for producing a CClF₂ CF₃ enrichedproduct may be integrated into an overall process (e.g., a thermal swingcycle process) whereby both of said products are provided.

DETAILS OF THE INVENTION

The present invention provides for the separation of CFC-115 fromHFC-125. A process is provided in accordance with this invention forproviding a high purity HFC-125 product which comprises the step ofcontacting mixtures of CClF₂ CF₃ (CFC-115) and CHF₂ CF₃ (HFC-125) with asorbent, selected from the group consisting of activated carbons,non-acidic silicate molecular sieves, and acidic inorganic molecularsieves at a temperature and pressure suitable for sorption, for a periodof time sufficient to remove a substantial amount of CFC-115. Prior toseparation, the HFC-125/CFC-115 mix preferably has a mole ratio of CHF₂CF₃ to CClF₂ CF₃ of at least about 9:1; more preferably a mole ratio ofat least about 19:1; and most preferably a mole ratio of at least about99:1.

A mixture of HFC-125 and CFC-115 may result, for example, from thehydrogenolysis of CFC-115 in the presence of catalysts containingplatinum-group metals at an elevated temperature (e.g., 320° C.).Unreacted starting material may be recycled and reacted further toproduce additional HFC-125. Additional impurities may also be present insuch products. Distillation is typically used in order to removeimpurities such as hydrogen fluoride, hydrogen chloride, and tars toproduce a product which has at least about 90 mole percent HFC-125.Further purification according to this invention may then beadvantageously employed. This invention can thus be adapted to providean improvement to a process for producing pure quantities of HFC-125.

Some embodiments of this invention use activated carbon as the sorbent.Commercially available activated carbon may be used. The effectivenessof the process can be influenced by the particular activated carbonemployed. Moreover, the sorption efficiency and sorption capacity of anactivated carbon bed depends upon the particle size of an activatedcarbon in a dynamic flow system. Preferably, the activated carbon has aparticle size range of from about 4 to 325 mesh (from about 0.044 to4.76 millimeters). More preferably, the activated carbon has a particlesize range of from about 6 to 100 mesh (from about 0.149 to 3.36millimeters). Most preferably, the activated carbon has a particle sizerange of from about 10 to 30 mesh (from about 0.595 to 2.00millimeters).

An activated carbon obtained having a particle size range of about0.074×0.297 millimeters (50×200 mesh) is available from the Barneby &Sutcliffe Corp. as Activated Carbon Type UU (natural grain, coconutshell based). An activated carbon having a particle size of 0.595millimeters×1.68 millimeters (12×30 mesh) is available from the CalgonCorporation as Calgon BPL (bituminous coal based) activated granularcarbon. An activated carbon having a particle size range of about0.450×1.68 millimeters (12×38 mesh) is available from Barneby &Sutcliffe Corp. as Barneby & Sutcliffe Corp. Activated Carbon Type PE(natural grain, coconut shell carbon). An activated carbon having aparticle size range of about 0.297×0.841 millimeters (20×50 mesh) isavailable from Westvaco as Microporous Wood-Base Granular Carbon.

Acid washed carbons are preferred. (See, e.g., U.S. Pat. No. 5,136,113for examples of acid washing.) However, the carbon can contain limitedamounts of various materials (e.g., alkali metals) so long as they donot destroy the ability of the carbon to preferentially sorb CFC-115.

Some embodiments of this invention use inorganic molecular sieves.Molecular sieves are well known in the art and are defined in R.Szostak, Molecular Sieves--Principles of Synthesis and Identification,Van Nostrand Reinhold, page 2 (1989). The inorganic molecular sievesused for preferentially sorbing CFC-115 in accordance with thisinvention include various silicates (e.g., titanosilicates, silicalitesand zeolites such as Zeolite Y, Zeolite ZSM-5, and Zeolite ZSM-8),metallo-aluminates and aluminophosphates, as well as other inorganicmolecular sieve materials. The molecular sieves useful in the inventionare either acidic or are non-acidic silicates, (i.e., all inorganicsilicate molecular sieves are included as suitable sorbents for thisinvention) and will typically have an average pore size of from about0.3 to 1.5 nm. Preferably, the average pore size is greater than 0.5 nm.

Acid forms of molecular sieves can be prepared by a variety oftechniques including ammonium exchange followed by calcination, directexchange of alkali ions for protons using mineral acids or ionexchangers, and by introduction of polyvalent ions (for a discussion ofacid sites in zeolites see J. Dwyer, "Zeolite, Structure, Compositionand Catalysis" in Chemistry and Industry, Apr. 2, 1984). The acid sitesproduced are generally believed to be of the Bronsted (proton donating)type or of the Lewis (electron pair accepting) type. Bronsted types aregenerally produced by deammoniation at low temperatures, exchange withprotons, or hydrolysis of polyvalent cations. Lewis sites are believedto derive from dehydroxylation of the H-molecular sieves or from thepresence of polyvalent ions. In the acidic molecular sieves of thepresent invention, Bronsted and/or Lewis acid sites can be present.

Some embodiments of this invention use non-acidic silicates (e.g.,silicalite) molecular sieves. Without limiting the invention to aparticular theory of operation, it is believed that non-acidicsilicalite molecular sieves, especially silicalite having an averagepore size of from 0.5 nm to about 0.6 nm, have size exclusion propertiesas well as sorption properties which facilitate the preferential removalof CFC-115.

Binders for molecular sieve particles may be used so long as they do notdestroy the ability of the sieve to perferentially sorb CFC-115. Forexample, some clays appear to be inappropriate binders.

The Sanderson electronegativity model (see, R. T. Sanderson, "ChemicalBonds and Bond Energy" 2nd ed., Academic Press, New York, 1976)furnishes a useful method for classifying inorganic molecular sievesbased on their chemical composition. The preferential sorption ofpentafluoroethanes by certain molecular sieves can be correlated withtheir intermediate electronegativity (i.e., their "Sint") as determinedby the Sanderson method based on chemical composition. For example,Zeolite Y molecular sieves with Sints greater than 2.8 (i.e., moreelectronegative or more acidic) may be used in accordance with thisinvention for increasing the mole ratio of CF₃ CHF₂ relative to CF₃CClF₂ by removing a substantial amount of CF₃ CClF₂ ; and/or forincreasing the mole ratio of CF₃ CClF₂ relative to CF₃ CHF₂ by desorbingsorbed CF₃ CClF₂ (i.e., CF₃ CClF₂ is believed to sorb more strongly thanCF₃ CHF₂ on Zeolite Y sieves with Sints greater than 2.8). Conversely,Zeolite Y molecular sieves with Sints no greater than 2.8 (i.e., lesselectronegative or more basic) may be used for increasing the mole ratioof CF₃ CClF₂ relative to CF₃ CHF₂ by removing a substantial amount ofCF₃ CHF₂ ; and/or for increasing the mole ratio of CF₃ CHF₂ relative toCF₃ CClF₂ by desorbing sorbed CF₃ CHF₂ (i.e., CF₃ CHF₂ is believed tosorb more strongly than CF₃ CClF₂ on Zeolite Y sieves with Sints lessthan 2.8). Example Sint values with calculated separation factors overforms of Zeolite Y of varying acidity/basicity are provided in Table A.

                  TABLE A                                                         ______________________________________                                        Intermediate Sanderson                                                        Electronegativities and Calculated Separation                                 Factors for Selected Zeolite Y Molecular Sieves                                                   Calculated.sup.a Separation                               Cation       Sint   Factor (115/125) at 50° C.                         ______________________________________                                        Cs.sup.+     2.37   0.0202                                                    Rb.sup.+     2.45   0.0382                                                    K.sup.+      2.53   0.0479                                                    Na.sup.+     2.58   0.115                                                     H.sup.+      2.96   2.36                                                      H.sup.+ /HFC-23.sup.b                                                                      3.03   2.63                                                      ______________________________________                                         .sup.a Extrapolation of ln(retention time) vs. 1/T                            .sup.b Preparation of this material is described in Example 7            

Suitable temperatures for sorption using activated carbon or inorganicmolecular sieves range from about -20° C. to about 300° C. Suitablepressures for sorption range from about 10 kPa to about 3000 kPa.

Contact with sorbent should be sufficient to achieve the desired degreeof HFC-125 enrichment. Preferably, the contact is sufficient to providea product wherein the amount of CFC-115 relative to HFC-125 in theproduct is no more than 50% of the amount of CFC-115 relative to HFC-125in the initial mixture. A particularly advantageous embodiment of thisinvention involves providing sufficient sorbent contact to produce CHF₂CF₃ of at least about 99.9 mole percent purity. This is facilitated byusing an initial mixture consisting essentially of CFC-115 and HFC-125.

This invention can be practiced with the sorbent contained in astationary packed bed through which the process stream whose componentsneed separation is passed. Alternatively, it can be practiced with thesorbent applied as a countercurrent moving bed or as a fluidized bedwhere the sorbent itself is moving. It can be applied with the sorbentcontained as a stationary packed bed but the process configured as asimulated moving bed, where the point of introduction to the bed of theprocess stream requiring separation is changed, such as may be effectedusing appropriate switching valves.

The production of purified CHF₂ CF₃ may be accompanied by the productionof other products which are enriched with regard to the concentration ofone or more other components of the initial mixture. Products enrichedwith respect to some compounds (e.g., CFC-115) are commonly obtained bydesorption following CHF₂ CF₃ purification. Desorption of componentsheld by the sorbent may be effected with the sorbent left in place, orthe sorbent may be removed and the desorption effected remotely fromwhere the sorption step occurred. These desorbed components may exit thesorbent section in a direction either co-current (in the same directionas the original stream requiring separation was fed) or countercurrent(in the opposite direction of the original stream requiring separation).Such desorption may be effected with or without the use of asupplemental purge liquid or gas flow, this purge material being any oneof the component materials, or some appropriate alternative material,similarly fed either co-currently or countercurrently.

In general, desorption can be effected by changing any thermodynamicvariable which is effective in removing the sorbed components from thesorbent. For example, sorption and desorption may be effected using athermal swing cycle, (e.g., where after a period of sorption, thesorbent is heated externally through the wall of the vessel containingit, and/or by the feeding of a hot liquid or gas into the sorbent, thehot gas being either one of the component materials or alternativematerials). Alternatively, the trace components can be removed by usinga pressure swing cycle or vacuum swing cycle (e.g., where after a periodof sorption, the pressure is sufficiently reduced, in some embodimentsto a vacuum, such that sorbed components are desorbed). Alternatively,the sorbed components can be removed by use of some type of strippinggas or liquid, fed co-currently or countercurrently to the originalprocess feed material. The stripping material may be one of the processfeed materials or another material such as nitrogen.

One or several beds of sorbent may be used. Where several beds are used,they may be combined in series or in parallel. Also, where several bedsare used, the separation efficiency may be increased by use of cyclingzone sorption, where the pressure and or the temperatures of the bedsare alternately raised and lowered as the process stream is passedthrough.

Practice of the invention will be further apparent from the followingnon-limiting Examples.

EXAMPLE 1

Metal tubing (0.19 inch I.D.×12 inch, 0.46 cm I.D.×30.5 cm) was packedwith a carbon sorbent, installed in a gas chromatograph with a flameionization detector. Helium was fed as a carrier gas at 33 sccm(5.5×10⁻⁷ m³ /s). Samples of CClF₂ CF₃ (CFC-115) and CHF₂ CF₃ (HFC-125)were then injected into the carrier stream. The results of theseexperiments are shown in Table 1. These data show that in each case thecompounds had different retention times, and thus may be separated usingthe carbons of this Example.

                  TABLE 1                                                         ______________________________________                                                          Retention                                                   Temp.      V(He)            Time (min.)                                                                            Separation                               Carbon °C.                                                                            sccm     Spl. μl                                                                          125.sup.a                                                                           115.sup.b                                                                          Factor.sup.c                         ______________________________________                                        A      200     33.2     200   2.78  6.04 2.17                                        200     33.2     250   2.74  5.94 2.17                                        150     33.2     100   10.18 24.32                                                                              2.39                                 B      200     33.2     100   1.51  3.99 2.64                                 ______________________________________                                         A  Carbon used was Barneby & Sutcliffe Type UU (3.85 g)                       B  Carbon used was Calgon BPL (2.59 g)                                        Temp.  Temperature of packed column in °C.                             V(He)  flow of helium in sccm                                                 Spl. = sample size of injection, in microliters                               .sup.a 125 = CF.sub.3 CHF.sub.2                                               .sup.b 115 = CF.sub.3 CClF.sub.2                                              .sup.c Separation Factor  115 retention time/125 retention time          

EXAMPLE 2

A packed tube (26 cm×2.12 cm I.D.) containing Barneby and Sutcliffe typeUU carbon (59.6 g, 50×200 mesh) was purged with nitrogen continuouslyfor several hours at 250° C. and at 1 atmosphere pressure. While stillbeing purged with nitrogen, the bed was cooled and was maintained at198° C. HFC-125 containing 4116 ppm CFC-115 was then fed to the bed at29 g/h. The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Time (min.)                                                                           HFC-125 in.sup.a                                                                           HFC-125 out.sup.b                                                                        CFC-115 out.sup.c                             ______________________________________                                         0      0            0          --                                            35      0.141        0          0                                             69      0.278        0.137      0.01                                          75      0.302        0.161      0.11                                          81      0.326        0.185      0.38                                          87      0.351        0.210      0.67                                          93      0.375        0.234      0.84                                          ______________________________________                                         .sup.a HFC-125 in represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 fed to the column.                                         .sup.b HFC125 out represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 exiting the column.                                        .sup.c CFC115 out represents the instantaneous concentration of the           CF.sub.3 CClF.sub.2 in the HFC125 exiting the column, expressed as a          multiple of the 4116 ppm feed (e.g., 0.5 would equal a 2058 ppm CFC115        concentration in the HFC125 effluent). A zero is less than the detection      limit of about 1 ppm.                                                    

The HFC-125 first began exiting the column at about 35 min., after about0.141 moles of HFC-125 had been fed. The HFC-125 flow breakthrough wassharp, and the outlet flow matched the inlet flow virtually immediately.The initial breakthrough of CFC-115 was detected at 69 min. After this93 min. run, the packed tube was purged with nitrogen at 250° C., andwas ready for further use. This example shows that carbon willselectively hold back CFC-115 allowing HFC-125 containing less than 10ppm of CFC-115 followed by HFC-125 containing reduced CFC-115concentrations to be obtained.

EXAMPLE 3

A packed tube (26 cm×2.12 cm I.D.) containing Barneby and Sutcliffe typeUU carbon (59.6 g, 50×200 mesh) was purged with nitrogen continuouslyfor several hours at 250° C. and at 1 atmosphere pressure. While stillbeing purged with nitrogen, the bed was cooled and was maintained at198° C. HFC-125 containing 4116 ppm CFC-115 was then fed to the bed at14.8 g/h. The results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Time (min.)                                                                           HFC-125 in.sup.a                                                                           HFC-125 out.sup.b                                                                        CFC-115 out.sup.c                             ______________________________________                                         0      0            0          --                                            53      0.109        0          0                                             56      0.115        0.006      0.01                                          62      0.128        0.019      0.01                                          68      0.140        0.031      0.02                                          74      0.152        0.043      0.04                                          80      0.165        0.056      0.17                                          86      0.177        0.068      0.45                                          92      0.190        0.081      0.71                                          ______________________________________                                         .sup.a HFC-125 in represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 fed to the column.                                         .sup.b HFC125 out represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 exiting the column.                                        .sup.c CFC115 out represents the instantaneous concentration of the           CF.sub.3 CClF.sub.2 in the HFC125 exiting the column, expressed as a          multiple of the 4116 ppm feed (e.g., 0.5 would equal a 2058 ppm CFC115        concentration in the HFC125 effluent). A zero is less than the detection      level of about 1 ppm.                                                    

The HFC-125 first began exiting the column at about min., after about0.109 moles of HFC-125 had been fed. The HFC-125 flow breakthrough wassharp, and the outlet flow matched the inlet flow virtually immediately.The initial breakthrough of CFC-115 was detected at 56 min. After this92 min. run, the packed tube was purged with nitrogen at 250° C. and wasready for further use. This example shows that carbon will selectivelyhold back CFC-115 allowing HFC-125 containing less than 10 ppm ofCFC-115 followed by HFC-125 containing reduced CFC-115 concentrations tobe obtained.

EXAMPLE 4

This is an example of a thermal swing cycle alternating a sorption stepwith desorption step. The column and carbon packing are the same asthose used in Example 2 above. During the sorption step, HFC-125containing 4115 ppm CF₃ CClF₂ (CFC-115) was fed to the carbon bed at 25°C. and 1 atm. (100 kPa), and with a HFC-125 flow of 37.6 g/h. When theCFC-115 started to break through at the other end of the column, theflow of high 115 concentration feed was stopped and the column washeated to 150° C. As the temperature was raised from 25° C. to 150° C.,HFC-125 containing less than 1 ppm 115 was fed in the directioncountercurrent to the original feed at 4.5 g/h and at 1 atm. (100 kPa).The gas generated from the heating was vented from the column in thedirection countercurrent to the original direction of feed, so as tokeep the back pressure at 1 atm. (100 kPa). Both sides of the columnwere then closed, the bed was cooled to 23° C. (causing a partialvacuum). The pressure was then brought back to 1 atm. (100 kPa) usingthe high CFC-115 content HFC-125, and the sorption cycle was startedagain. The sorption and desorption steps were then repeated.

Table 4 shows the results from the first sorption step at 27° C.

                  TABLE 4                                                         ______________________________________                                        Time (min.)                                                                           HFC-125 in.sup.a                                                                           HFC-125 out.sup.b                                                                        CFC-115 out.sup.c                             ______________________________________                                         0      0.000        0.000      --                                             40     0.101        0.000      --                                             46     0.116        0.015      0.03                                          128     0.323        0.222      0.03                                          134     0.338        0.237      0.05                                          140     0.353        0.252      0.11                                          ______________________________________                                         .sup.a HFC-125 in represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 fed to the column.                                         .sup.b HFC125 out represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 exiting the column.                                        .sup.c CFC115 out represents the instantaneous concentration of the           CF.sub.3 CClF.sub.2 in the HFC125 exiting the column, expressed as a          multiple of the 4116 ppm feed (e.g., 0.5 would equal a 2058 ppm CFC115        concentration in the HFC125 effluent).                                   

Breakthrough of HFC-125 occurred at about 40 min., after about 0.10moles of HFC-125 had been fed. The breakthrough was very sharp; theoutlet flow reaching the inlet flow almost immediately. The initialbreakthrough of the CFC-115 was detected at about 46 min. At 140 min.the high CFC-115 content HFC-125 was stopped.

The result of the desorption step which followed is shown in Table 5.

                  TABLE 5                                                         ______________________________________                                        Time   Temp.                                                                  (min.) °C.                                                                            HFC-125 in.sup.a                                                                         HFC-125 out.sup.b                                                                       CFC-115 out.sup.c                         ______________________________________                                         0      27     0.000      0.000     --                                        12      32     0.007      0.029     1.53                                      23      65     0.014      0.063     1.69                                      36      71     0.022      0.073     2.06                                      47      82     0.029      0.093     1.82                                      59     125     0.036      0.134     2.20                                      71     150     0.044      0.152     2.40                                      83     150     0.052      0.160     2.3                                       95     150     0.059      0.168     2.02                                      107    150     0.066      0.175     1.97                                      119    150     0.074      0.183     0.51                                      130    150     0.081      0.191     0.21                                      ______________________________________                                         .sup.a HFC-125 in represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 fed to the column.                                         .sup.b HFC125 out represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 exiting the column.                                        .sup.c CFC115 out represents the instantaneous concentration of the           CF.sub.3 CClF.sub.2 in the HFC125 exiting the column, expressed as a          multiple of the 4116 ppm feed (e.g., 0.5 would equal a 2058 ppm CFC115        concentration in the HFC125 effluent).                                   

Beginning at 71 min., as the temperature was increased from 27° C. to150° C., the lower trace component HFC-125 was fed at 4.5 g/h. At 130min., the HFC-125 flow was stopped, the column valved off at both ends,and the column cooled to 27° C.

This example shows the use of temperature swing cycle as a processconcept.

EXAMPLE 5

This is an example of a thermal swing cycle, alternating a sorption stepwith desorption step. The column is the same as that used in Example 2above but packed with Calgon BPL carbon (46.1 g; 12×30 mesh). During thesorption step, HFC-125 containing 4115 ppm CF₃ CClF₂ (CFC-115) was fedto the carbon bed at 25° C., and at 1 atm. (100 kPa), and with a HFC-125flow of 32.7 g/h. When the CFC-115 started to break through at the otherend of the column, the flow of high 115 concentration feed was stoppedand the column was heated to 150° C. As the temperature was raised from25° C. to 150° C., HFC-125 containing less than 1 ppm 115 was fed in thedirection countercurrent to the original feed at 9.0 g/h and at 1 atm.(100 kPa). The gas generated from the heating was vented from the columnin the direction countercurrent to the original direction of feed, so asto keep the back pressure at 1 atm. (100 kPa). Both sides of the columnwere then closed, the bed was cooled to 25° C. (causing a partialvacuum). The pressure was then brought back to 1 atm. (100 kPa) usingthe high CFC-115 content HFC-125, and the sorption, desorption cycle wasstarted again.

Table 7 shows the results from the first sorption step at 25° C.

                  TABLE 7                                                         ______________________________________                                        Time (min.)                                                                           HFC-125 in.sup.a                                                                           HFC-125 out.sup.b                                                                        CFC-115 out.sup.c                             ______________________________________                                         0      0.000        0.000      --                                            19      0.086        0.000      --                                            25      0.114        0.028      0.02                                          83      0.375        0.289      0.02                                          89      0.404        0.318      0.14                                          ______________________________________                                         .sup.a HFC-125 in represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 fed to the column.                                         .sup.b HFC125 out represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 exiting the column.                                        .sup.c CFC115 out represents the instantaneous concentration of the           CF.sub.3 CClF.sub.2 in the HFC125 exiting the column, expressed as a          multiple of the 4116 ppm feed (e.g., 0.5 would equal a 2058 ppm CFC115        concentration in the HFC125 effluent).                                   

Breakthrough of HFC-125 occurred at about 19 min., after about 0.08moles of HFC-125 had been fed. The breakthrough was very sharp; theoutlet flow reaching the inlet flow almost immediately. The initialbreakthrough of the CFC-115 was detected at about 25 min. At 89 min. thehigh CFC-115 content HFC-125 was stopped.

The results of the desorption step which followed are shown in Table 8.

                  TABLE 8                                                         ______________________________________                                        Time   Temp.                                                                  (min.) °C.                                                                            HFC-125 in.sup.a                                                                         HFC-125 out.sup.b                                                                       CFC-115 out.sup.c                         ______________________________________                                         0      25     0.000      0.000     --                                        12      44     0.015      0.040     1.28                                      23      77     0.030      0.091     1.55                                      36     120     0.045      0.144     2.20                                      47     155     0.060      0.175     2.76                                      59     155     0.076      0.190     2.36                                      71     155     0.091      0.205     1.76                                      83     155     0.106      0.220     1.01                                      95     155     0.121      0.235     0.53                                      107    155     0.135      0.250     0.23                                      119    155     0.150      0.265     0.09                                      ______________________________________                                         .sup.a HFC-125 in represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 fed to the column.                                         .sup.b HFC125 out represents the total running sum of the moles of            CF.sub.3 CHF.sub.2 exiting the column.                                        .sup.c CFC115 out represents the instantaneous concentration of the           CF.sub.3 CClF.sub.2 in the HFC125 exiting the column, expressed as a          multiple of the 4116 ppm feed (e.g., 0.5 would equal a 2058 ppm CFC115        concentration in the HFC125 effluent).                                   

Beginning at 0 min., as the temperature was increased from 25° C. to155° C., the lower trace component HFC-125 was fed at 9.0 g/h. At 119min., the HFC-125 flow was stopped, the column valved off at both ends,and the column cooled to 25° C.

This example shows the use of temperature swing cycle as a processconcept.

EXAMPLE 6

Metal tubing 0.18" (4.6 mm) I.D.×2 ft. (0.51 m) was packed with zeolitesorbents as indicated in Table 9, and installed in a gas chromatographwith a flame ionization detector. The columns were heated at 200° C. inflowing helium for a minimum of 12 hr. Helium was fed as a carrier gasat 20 sccm (3.3×10⁻⁷ m³ /g). Samples (25 μL) of CFC-115 and HFC-125 werethen injected into the carrier stream at various selected temperatures.The results of these experiments are shown in Table 9. These data showthat in each case the compounds had different retention times, and thusmay be separated using the sorbents of this Example.

                  TABLE 9                                                         ______________________________________                                                          Retention                                                                     Times (min.)                                                Zeolite                                                                             Temp. °C.                                                                          115/125    Separation Factor.sup.a                          ______________________________________                                        HY    190         2.55/1.70  1.49                                             HY    200         2.20/1.48  1.49                                             HY    210         1.91/1.33  1.41                                             NaY   190         14.3/34.9  0.41                                             NaY   200         12.3/28.1  0.44                                             NaY   210         10.3/22.4  0.46                                             CaA   190         0.21/29.3  0.007                                            CaA   200         0.19/23.1  0.007                                            CaA   210         0.18/16.9  0.011                                            ______________________________________                                         .sup.a Separation Factor = 115 Retention Time/125 Retention Time         

EXAMPLE 7

Metal tubing 0.25" (6.4 mm) O.D.×4.5 in. (11.4 cm) was packed withsorbents as indicated in Table 10, and installed in a gas chromatographwith a flame ionization detector. The columns were heated at 200° C. inflowing helium for a minimum of 12 hours. Helium was fed as a carriergas at 30 sccm (5.0×10⁻⁷ m³ /s). Samples (25 μL) of CFC-115 and HFC-125were then injected into the carrier stream at various selectedtemperatures. The results of these experiments are shown in Table 10.These data show that in each case the compounds had different retentiontimes, and thus may be separated using the sorbents of this Example.

                  TABLE 10                                                        ______________________________________                                        Sorbent      Temp. °C.                                                                        Separation Factor.sup.a                                ______________________________________                                        C-111-1.sup.b                                                                              200       2.48                                                   C-111-2.sup.c                                                                              200       1.98                                                   C-111-3.sup.d                                                                              200       1.97                                                   Cs-Y         200       0.2                                                    Cs-Y         210       0.23                                                   Cs-Y         220       0.24                                                   ETS-10       220       0.3                                                    H-ZSM-8      150       1.63                                                   H-ZSM-8      200       1.46                                                   K-Y          190       0.21                                                   K-Y          210       0.24                                                   K-Y          220       0.26                                                   Li-Y         200       0.71                                                   H-Y/AlF.sub.3 .sup.e                                                                        75       1.8                                                    H-Y/AlF.sub.3 .sup.e                                                                       100       1.77                                                   H-Y/AlF.sub.3 .sup.e                                                                       200       1.57                                                   H-Y/AlF.sub.3 -2.sup.f                                                                      50       0.39                                                   H-Y/AlF.sub.3 -2.sup.f                                                                     100       0.67                                                   H-Y/AlF.sub.3 -2.sup.f                                                                     200       0.8                                                    H-Y/HFC-23.sup.g                                                                            75       2.37                                                   H-Y/HFC-23.sup.g                                                                           100       2.16                                                   H-Y/HFC-23.sup.g                                                                           200       1.61                                                   Na-Mordenite 200       0.28                                                   H-Mordenite.sup.h                                                                          200       1.74                                                   H-Mordenite.sup.i                                                                          200       1.93                                                   H-ZSM-5      200       1.31                                                   H-ZSM-5      150       1.53                                                   H-ZSM-5      170       1.46                                                   H-ZSM-5      200       1.35                                                   Rb-X         200       0.39                                                   Rb-Y         210       0.23                                                   Rb-Y         220       0.25                                                   Silicalite.sup.j                                                                           200       1.59                                                   Silicalite.sup.j                                                                           175       1.78                                                   Silicalite.sup.j                                                                           150       1.91                                                   Silicalite.sup.k                                                                           200       1.59                                                   Silicalite.sup.k                                                                           175       1.78                                                   Silicalite.sup.k                                                                           150       1.92                                                   Silicalite.sup.l                                                                           200       1.57                                                   Silicalite.sup.l                                                                           175       1.71                                                   Silicalite.sup.l                                                                           150       1.83                                                   Silicalite.sup.m                                                                           200       1.64                                                   Silicalite.sup.m                                                                           175       1.83                                                   Silicaliten.sup.m                                                                          150       2.25                                                   ______________________________________                                         .sup.a Separation Factor = 115 Retention Time/125 Retention Time.             .sup.b An activated, high surface area carbon was washed first with           hydrochloric acid, then with distilled water until the washings were free     of residual chloride, and then dried overnight at 95° C.. The          carbon was crushed with a mortar and pestle and the fraction passing          through a 20 mesh (0.85 mm) sieve but not a 40 mesh (0.425 mm) sieve was      collected and used.                                                           .sup.c An activated, high surface area carbon was washed by stirring it i     a refluxing dilute solution of nitric acid for one hour, then collected       and washed with copious amounts of water and dried overnight at 95.degree     C.. The sample was crushed with a mortar and pestle and the fraction          passing through a 20 mesh (0.85 mm) sieve but not a 40 mesh sieve (0.425      mm) was collected and used.                                                   .sup.d An activated, high surface area carbon was washed by stirring it i     a refluxing dilute solution of nitric acid for one hour, then collected       and washed with copious amounts of water. A slurry of this carbon and 0.1     sodium hydroxide was made and stirred for 16 h. The caustic solution was      decanted and replaced by distilled water. After 24 h the water was            decanted and the carbon washed with three portions of distilled water,        then dried overnight at 95° C.. The sample was crushed with a          mortar and pestle and the fraction passing through a 20 mesh (0.85 mm)        sieve but not a 40 mesh (0.425 mm) sieve was collected and used.              .sup.e Granulated HY (10 g) was dried at 500° C. and impregnated       with 5 wt % AlF.sub.3 using the collidininium salt dissolved in               acetonitrile. After 30 min. the solution was evaporated to dryness in a       vacuum and the recovered material was heated to 600° C. in flowing     nitrogen to drive out the collidinium fluoride and leave behind the           betaAlF.sub.3 phase. Analysis shows 2.76% F.                                  .sup.f Granulated HY (10 g) was dried at 500° C. and impregnated       with 5 wt % AlF.sub.3 using the tetramethylammonium salt dissolved in         acetonitrile. After 30 min. the solution was evaporated to dryness in a       vacuum and the recovered material was heated to 600° C. in flowing     nitrogen to drive out the tetramethylammonium fluoride and leave behind a     mixture of the eta and betaAlF.sub.3 phases.                                  .sup.g Granulated (+20/-30 mesh, (0.83 to 0.54 mm)) HY (6 g) was placed i     a quartz tube containing a frit in a vertically mounted tube furnace. The     sample was heated to 425° C. at 5° C./min. under flowing        nitrogen. It was held at 425° C. for one hour with flowing             nitrogen. At that point, the gas was switched to CHF.sub.3 (HFC23) and        held for another hour at 425° C.. The sample was then cooled under     flowing nitrogen. XRD analysis showed crystalline zeolite Y and               betaAlF.sub.3. Chemical analysis gave: 30.3% Si, 10.8% Al, and 21.2% F.       .sup.h The SiO.sub.2 :Al.sub.2 O.sub.3 ratio was 20:1.                        .sup.i The SiO.sub.2 :Al.sub.2 O.sub.3 ratio was 35:1.                        .sup.j DuPont silicalite containing 10% Bentonite as a binder.                .sup.k DuPont silicalite containing 20% alumina as a binder.                  .sup.l DuPont silicalite containing 20% Bentonite as a binder.                .sup.m Linde silicalite                                                  

Particular aspects of the invention are illustrated in the Examples.Other embodiments of the invention will become apparent to those skilledin the art from a consideration of the specification or practice of theinvention disclosed herein. It is understood that modifications andvariations may be practiced without departing from the spirit and scopeof the novel concepts of this invention. It is further understood thatthe invention is not confined to the particular formulations andexamples herein illustrated, but it embraces such modified forms thereofas come within the scope of the claims.

What is claimed is:
 1. A process for separating a mixture of CHF₂ CF₃and CClF₂ CF₃ to provide a product wherein the mole ratio of CHF₂ CF₃relative to CClF₂ CF₃ is increased, comprising the step of: contactingsaid mixture with a sorbent for CClF₂ CF₃ selected from the groupconsisting of (i) acidic inorganic molecular sieves, (ii) non-acidicsilicate molecular sieves, and (iii) activated carbons, at a temperaturewithin the range of -20° C. to 300° C. and a pressure within the rangeof 10 kPa to 3000 kPa and for a period of time sufficient to remove asubstantial amount of the CClF₂ CF₃ and increase the mole ratio of CHF₂CF₃ to CClF₂ CF₃.
 2. The process of claim 1 wherein prior to separationthe mixture has a mole ratio of CHF₂ CF₃ to CClF₂ CF₃ of at least about9:1; and wherein a product is produced wherein the amount of CClF₂ CF₃relative to the amount of CHF₂ CF₃ is no more than 50% of the relativeamount of CClF₂ CF₃ in the mixture prior to separation.
 3. The processof claim 2 wherein a mixture consisting essentially of CClF₂ CF₃ andCHF₂ CF₃ is separated to provide CHF₂ CF₃ of at least about 99.9 molepercent purity.
 4. A process for separating a mixture of CHF₂ CF₃ andCClF₂ CF₃ to provide a product wherein the mole ratio of CClF₂ CF₃relative to CHF₂ CF₃ is increased comprising the step of: contactingsaid mixture with a sorbent for CClF₂ CF₃ selected from the groupconsisting of (i) acidic inorganic molecular sieves, (ii) non-acidicsilicate molecular sieves, and (iii) activated carbons, at a temperaturewithin the range of -20° C. to 300° C. and a pressure within the rangeof 10 kPa to 3000 kPa and for a period of time sufficient to remove asubstantial amount of the CClF₂ CF₃ ; and desorbing sorbed CClF₂ CF₃ toprovide a product which is enriched therewith.
 5. The process of claim1, claim 2, claim 3, or claim 4 wherein the sorbent is a zeolite havingan average pore size of from 0.3 to 1.5 nanometers.
 6. The process ofclaim 5 wherein the sorbent is Zeolite Y having an intermediateelectronegativity greater than 2.8.
 7. The process of claim 5 whereinthe average pore size is greater than 0.5 nanometers.
 8. The process ofclaim 1, claim 2, claim 3, or claim 4 wherein the sorbent is anon-acidic silicalite having an average pore size of from 0.5 nm toabout 0.6 nm.
 9. The process of claim 1, claim 2, claim 3, or claim 4wherein the sorbent is an activated carbon.
 10. The process of claim 9wherein the activated carbon is acid washed.